LED packages serve important functions for LED chips. For example, the LED packages protect the LED chips from the environment, and allow the LED chips to interface electrically and thermally with printed circuit boards. Furthermore, LED packages provide mechanical support, provide the appropriate electrical connections, assist with heat dissipation, and enhance the light emission efficiency from the LED chip.
FIG. 1 illustrates a conventional LED package 100. The package 100 consists of a LED die 160 attached to a ceramic substrate 110b (e.g., AlN or Al2O3) via a top electrode 190. The LED die 160, which comprises a LED substrate 140, a light emitting layer 130, and a phosphor layer 120, is conventionally attached to the LED substrate 140 with die-attach epoxy or solder (not shown). The light emitting layer 130 comprises a p-type layer, an active layer and an n-type layer. After the LED die 160 is attached to the substrate 110b, a separate process is required to attach a bond wire 150 which electrically connects the LED die 160 to the top electrode 190 on the substrate 110b. There are electrical conducting vias 110a built into the ceramic substrate 110b to connect the top electrode 190 and electrical contact pads 170a and thermal pad 170b. Thermal pad 170b facilitates heat dissipation from the LED package 100 to a heat-sink (not shown). Finally, a molded silicone dome 180 is formed on top of the LED die 160. A completed conventional LED package 100 is then ready for use and surface-mountable to printed circuit boards or a heat-sink.
One issue with a conventional LED package such as the one shown in FIG. 1 is the cost associated with using die-level processing and packaging techniques to fabricate the LED package. The U.S. Department of Energy published a report—Bardsley et al., “Manufacturing Roadmap—Solid State Lighting Research and Development” (August 2014)—which is incorporated herein by reference. The report breaks down various LED Cost Drivers for high-power LED packages and concluded that a majority of the costs are attributable to packaging costs associated with die-level processing (i.e., the costs associated with performing steps on each die on the wafer). According to the report, these packaging costs account for 61% of the total cost for high-power LED packages, with costs for performing wafer level processing and the materials for the substrate, epitaxy, and phosphor making up for the remainder of the total cost of the LED package. Forecasting ahead, the report predicted that the figure for high-power LED packages is only expected to drop to 54% of the total cost for high-power LED packages by 2020.
With most of the costs for manufacturing conventional LED packages tied to die-level processes, the report suggested that cost savings could be achieved by performing more of the packaging processes at the wafer level. Wafer-level processing of an LED package refers to packaging the LED while it is still part of the wafer; in contrast, die-level processing acts on each LED package individually.
As such, the report recognized the long-felt need for an improvement to conventional LED packages and their respective fabrication methods by performing packaging activities at a wafer level in order to reduce the costs for LED packages.
Another issue with the conventional LED package 100 is the exposure of the sidewalls 140a of LED substrate 140 when a LED with an absorbing substrate is used in the package. This amount of the exposed sidewalls 140a is determined by the height, h, of the LED die 160. The exposed sidewalls 140a compromise the efficiency of the LED package 100 because they absorb light emitted from the light emitting layer 130 when light is reflected within the silicone dome 180. To prevent the sidewalls 140a from absorbing light and thereby improve efficiency of light output, applying a reflective coating (not shown) to cover the sidewalls 140a of the LED substrate 140 is preferable.
Prior methods of replacing common semiconductor wafers with a “reconstituted” semiconductor wafer are well known. For example, Fuerget et al., U.S. Pat. No. 7,202,107, which is hereby incorporated by reference, discloses the concept of embedding semiconductor chips onto a plastic compound and forming the semiconductor component from the embedded chips. However, due to the difficulties in the manufacturing process, such a technique has never been applied in the manufacture of LED packages.
Accordingly, there remain long-felt needs to reduce the costs of producing LED packages and to improve the efficiency of the light output of LED packages.